This invention relates to mobile liquid containers, such as gasoline or other liquid product tanker trucks or rail cars, and more particularly to emergency shut-off or foot valves that are part of such mobile containers.
With reference to FIG. 7, fueling tanker trucks are typically constructed with an elongated under-carriage frame and an elongated, horizontal storage tank having a number of internally divided compartments with various unequal volume capacities to store and transport gasoline, fuel oil, aircraft fuels, or other volatile liquids and fuels. Gasoline tankers are typically bottom loaded through load only or load/unload couplers or adaptors 100 located below and toward the center of and longitudinally along the tanker undercarriage.
Each adaptor 100 communicates with the bottom of a respective storage compartment through an elongated 4" rigid delivery pipe 102 made of cast aluminum, bronze, or steel. The compartment end of the delivery pipe communicates with a compartment through an emergency poppet valve 104 (sometimes referred to as a foot valve) mounted in the compartment bottom and operated by an external handle. The adapter 100 at the end of the delivery pipe 102 releasably mates with a corresponding coupler on a delivery hose 106. The far end of delivery hose (not shown) couples into the below ground riser coupler associated with the below ground gasoline storage tank when liquid product is to be discharged from the tanker to the below ground storage tank.
Each tank emergency valve 104 includes a poppet valve that seats in a normally closed position within the coupler. The standard emergency valve 104 includes an operating handle that, when rotated to the fill position, rotates an internal actuator that raises the tank coupler poppet valve to allow liquid flow by gravity through the housing of valve 104 into the delivery pipe, through the delivery hose and into the top of the riser, drop tube, and storage tank below. The handle of valve 104 is coupled to the operator control handle of adapter 100 so that these handles operate together in ganged fashion. Vapor recovery lines (not shown) connected from the tank top back to the tanker manifold equalizes vapor pressures and stores vapors in the tanker that had been displaced from the top region of the below ground tank by the fill liquid.
Fill liquid enters the riser at a high rate, e.g. 340 gallons per minute. When the below ground tank reaches a predetermined fill level, conventional overfill prevention apparatus located in the drop tube greatly restricts or cuts off drop tube flow. The operator then rotates the adaptor 100 and emergency valve 104 fill handles to their closed positions which in turn shuts and seals the adaptor 100 and emergency tank valve poppet 104 closed. This action traps the fuel within the delivery pipe 102. Next, the operator disconnects the upstream end of the delivery hose 106 from the adaptor 100 at the downstream end of delivery pipe 102. Gasoline in the hose simply bleeds into the top of the riser as the operator lifts and "walks" the hose sections toward the riser. The hose is then disconnected at the riser and stowed on the tanker for transport to the next site.
Note the process purposely traps about 20 gallons of gasoline in the long delivery pipe 102 (and about 5 gallons in the short pipe 102) avoiding excessive air being forced down into the riser and drop tube when fill liquid flow next begins or air being forced into the tanker compartment during bottom filling process. However, this standard practice creates a dangerous and hazardous condition because delivery pipes extend along and adaptors are located at an exposed side of the tanker. It is known that tanker sides occasionally impact cars, other trucks, poles, or other objects when making turns on city streets or otherwise. This impact causes the shear fitting of the emergency valve 104 housing to shear thus dislocating the upstream delivery pipe end from the tank. Although no gasoline emits from the tanker compartment because the poppet remains closed, nevertheless the liquid product within the delivery pipe discharges from the now free (upstream) pipe end in liquid and vapor form at a high rate and sprays along the ground and in the air. Volatile vapors blanket the general area and liquid has been known to wet objects and people in the area. Fires and combustion are known to have resulted.